1. Field of the Invention
This invention relates to the analysis of a shaft vibration signal which arises in a large-sized rotary machine such as steam turbine and generator in a thermal or nuclear power plant. More particularly, it relates to a method and apparatus for monitoring the shaft vibration of a rotary machine wherein a shaft vibration signal developing during operation is analyzed in real time so as to clear up the cause of the shaft vibration.
As the capacities of rotary machines have become large, the shaft vibrations of the rotary machines have become an important subject in the operation maintenance. In a large-capacity steam turbine, the so-called shaft vibration phenomenon has come to present more and more complicated aspects on account of an increase in the weight of a rotor, an increase in the distance between the centers of bearings, and increases in the number of wheel chambers, etc. Recently, the start and stop of the turbine are frequently made. Therefore, abnormal vibrations attributed to a thermal unbalance etc. are more liable to occur that in case of continuing the operation under the steady state.
It is at the starting that an operator concentrates attention most. The disposal of the abnormal vibration at this time needs to be properly made so as not to lose the timing. Of course, the vibration monitoring in the steady state cannot be treated lightly.
Since a high precision and a high-speed processing are required of such analysis and monitoring of a shaft vibration signal, it is favorable to process the signal digitally and monitor the shaft vibration state.
This invention concerns a method and apparatus for loading data while automatically adjusting a sampling period in the case of analyzing the shaft vibration signal with a digital technique, in order to analyze at high speed and at high precision a rotational frequency component and fractional harmonic components or higher harmonic components thereof or a frequency component relating to a natural frequency.
2. Description of the Prior Art
The commonest expedient for monitoring the shaft vibration of a rotary member is a method in which the vibration amplitude of a detected shaft vibration signal itself is monitored. Since, however, the vibration of a certain specific frequency component due to the cause of abnormality, the monitoring of the vibration amplitude of the detected signal itself leads to the disadvantage that an appropriate monitoring of the shaft vibration is impossible.
On the other hand, a method in which a vibrational waveform is subjected to a Fourier analysis and grasped as a power spectrum is disclosed in U.S. Pat. No. 3,694,637 (Sept. 26, 1972, Method and Apparatus for Detecting Tool Wear). However, this method decides the time of the exchange of a tool by the comparison of the power spectrum with a reference power spectrum, and merely a digitized signal for the Fourier analysis is shown in FIG. 2 of the patent specification.
U.S. Pat. No. 3,641,550 (Feb. 8, 1972, Vibration-Monitoring Systems) teaches a vibration monitoring system for a gas turbine engine in the case of 3 shafts. Although the exchange of filters is disclosed, analog signal processings are performed to the last.
In Japanese Laid-open Patent Application No. 54-111871 filed by the same applicant (Japanese Patent Application No. 53-18486, laid open Sept. 1, 1979), a detected shaft vibration signal is analyzed on a frequency component which is in a predetermined relationship with a rotational frequency component, and the operation control of a rotary machine is made in accordance with a predetermined operation pattern on the basis of the analyzed result. Herein, however, the operation control under the assumption that the digital analytical result has been obtained is stated, and no reference is made to the loading of digitized data, that is, the relations between a sampling frequency and a rotational frequency or fractional harmonic components, etc.
This invention consists, in the loading of digitized data, in that the data are loaded with the smallest possible number of samples, and that even when the rotational frequency has fluctuated, the sampling frequency is automatically adjusted while holding an analytical precision, whereupon the analytical data are received. This measure is a very important one indispensable to the digital analysis.